The present invention relates to a fuel-air premixing device for a gas turbine, particularly for a gas turbine which is operates at a high gas temperature.
A known fuel-air premixing device for a gas turbine is disclosed in Japanese Patent Laid-Open No. 61-22127 which corresponds to the U.S. patent application Ser. No. 144,646, now U.S. Pat. No. 4,898,001, which was a Continuation application of U.S. application Ser. No. 752,680, now abandoned. This known premixing device has a plurality of bar-like fuel nozzles arranged circularly. The fuel emitted from these nozzles is gasified and mixed with combustion air so that a premixture of the fuel and air mixed at a moderate ratio and in good state is discharged from the outlet of the premixing device.
This known premixing device suffers from a problem in that, when the capacity of the premixing device is increased to suppress emission of NOx from a gas turbine incorporating this premixing device, a non-uniform flowing velocity distribution is developed in the radial direction at the outlet of the premixing device, with the result that the desired uniform distribution of concentration of fuel cannot be obtained. Another problem is that the premixing device of the type described has a practical limit in the reduction of the air supply rate. Namely, it is difficult to reduce the air supply rate when the fuel supply rate is decreased to meet a demand for light-load operation of the gas turbine. In consequence, the fuel-to-air ratio is decreased to cause an air-excess ratio to increased impractically, often resulting in troubles such that the flame in the premixing device becomes unstable and it might be blown out in the worst case.